The day started like a regular Sunday for Mohammad al-Daher, better known as Abu Azzam, the commander of the rebel Farouq Brigades in the vast swath of eastern Syria called the Jazira, a region that stretches from the Turkish border to the Iraqi frontier and encompasses the three provinces of Raqqa, Hasaka and Deir ez-Zor. He had a series of meetings in the morning in a number of locations in the bustling town of Tal Abyad on Syria’s border with Turkey as well as in the partially destroyed former police station that is the Farouq’s headquarters. And he was going to visit his mother.

By late afternoon, however, the burly 34-year-old Raqqa native would be lying in a hospital bed — wounded by members of the ultraconservative Islamist group Jabhat al-Nusra (which the U.S considers a terrorist organization with links to al-Qaeda). Abu Azzam’s targeting has blown open a sharp rift and long-brewing conflict between the more secular nationwide Farouq brigades and the Jabhat. The two groups are among the most effective, best organized and most well-known of the many military outfits aligned against Syrian President Bashar Assad — and the fight between them is just beginning.

Farouq has the upper hand in Tal Abyad, which lies opposite the Turkish city of Akcakale. It snatched the border crossing from Assad’s forces on Sept. 19, much to the chagrin of a number of other rebel groups — both secular units under the loose banner of the Free Syrian Army (FSA), as well as Islamist groups operating independently. It’s not the only border post controlled by the Farouq. The gateway to Idlib province, Bab al-Hawa, near the Turkish city of Reyhanli, is also in their hands. The Jabhat, on the other hand, were at the forefront of taking Raqqa city, farther to the south, the first provincial capital to fall to any rebel force.

By mid-afternoon, Abu Azzam stopped in to see his mother, Em Mohammad, in her modest first-floor apartment a short walk from the Farouq base. The young man stooped to kiss her right hand, he put his forehead to it before kissing her cheeks and embracing her warmly. “Finally, I see you!” she told him, gently scolding her son as he sat beside her. “You know the last time I saw him he was like this,” Em Mohammad said, picking up Abu Azzam’s two cell phones, holding one to each ear and pretending to issue orders into them, interspersing the talk of weapons and requests for battle updates with “Hi, mother, how are you, how is your health?” The half a dozen men in the room all laughed. “I’m sorry,” Abu Azzam told his mother, “but what can I do?”

Turkish coffee was served in delicate, thin-handled china cups. On this day Abu Azzam wasn’t in his unit’s military uniform. He was dressed in indigo jeans, a dark green crew-neck sweater, a black leather jacket and navy boat shoes. He has a Salafi-style black beard (without a mustache) that he frequently tugs at and a smile so broad and disarming that it seems like it takes up his whole face.

He reached for his pack of Winston Silver cigarettes before turning to his mother, a feisty, friendly woman in a long black dress and powder blue headscarf whom he bore a striking resemblance to. “Just so you don’t hear it elsewhere, they planted an [improvised explosive] device in my car yesterday,” he told her. Em Mohammad put her hand up to her mouth. She had lost Abu Hussein, the second of her three sons, on Feb. 20 in the battles for Raqqa province. He was also a member of the Farouq, a father of two little girls, and now her eldest son was telling her he had been targeted. “May God protect you,” she told him.

“Nobody dies before his time,” Abu Azzam said, repeating a common Arabic phrase. In a chilling premonition of what would happen just a few hours later, he said: “I know that I am going to be killed either by the regime or by the Jabhat. There is no difference, they are both dirty.”

The device consisted of several sticks of TNT wired to the ignition of a BMW vehicle Abu Azzam often travels in. A neighbor alerted the Farouq leader to the presence of the device.

Seated on the floor, Abu Azzam rattled off a laundry list of towns and cities he said the Farouq helped clear of Assad’s forces. “What did they liberate?” he said of the Jabhat. “They are just here to try and impose their rules on us.” He held up his cigarette: “They threatened to label me a kafir [unbeliever or apostate] because of this,” he said. (Some ultraconservatives consider smoking a sin.)

Some of the men in the room who had just returned from Raqqa city, relayed details of the Jabhat’s smear campaign there against Abu Azzam and the Farouq. “They’re calling us Farouq sarouk,” one said (sarouk roughly translated in this context means thief). “Some of them say that we are nonbelievers.”

It’s not the first time Abu Azzam has clashed with conservative Islamists. Before taking Tal Abyad, he was in charge of the Bab al-Hawa crossing hundreds of kilometers away. A Syrian Islamist extremist called Abu Mohamad al-Absi, who led a group of foreign jihadis who at one point controlled one of Bab al-Hawa’s two gates, wanted to raise the black banner over the border crossing, something Abu Azzam opposed. Al-Absi was kidnapped and killed in September 2012, most likely by the Farouq, although they haven’t admitted it. The jihadis retaliated in early January, killing Abu Azzam’s successor, Abu Ali, at Bab al-Hawa. In several meetings with TIME over the past year, Abu Azzam has repeatedly said the Farouq will not allow Islamic extremists to “hijack” the revolution.

There was a knock at the door. A cleric with a long gray beard, in a flowing white galabiya (a loose, floor-length robe) and a vest over it, entered the house. Em Mohammad and most of the men in the room were asked to sit in another room while Abu Azzam met the man. “Please wait with the chief of staff,” Abu Azzam said, laughing, referring to his mother. Other men in the Farouq jokingly call Em Mohammad “Anissa,” after Bashar Assad’s mother Anissa, a woman who some say acts as her son’s key adviser and is actually the real power behind the regime. That Em Mohammad is respected among the Farouq for her warmth, savvy and strength is without question, and those qualities would soon come to the fore in the hours ahead.

The meeting was brief and the sheik didn’t stay for lunch, which was placed on a black plastic sheet on the floor as is customary. Store-bought kebabs, grilled tomatoes and green peppers, as well as minted yogurt were laid out. Flat Arabic bread was passed around. “This is the first thing I’ve eaten all day,” Abu Azzam said. It was almost 4:30 p.m.

The three men seated around him, Bandar, Ramadan and Badr, were all old friends from the central city of Homs who studied at the university there. The four men all lived together before the Syrian revolution. When the uprising became armed, Abu Azzam, a fourth-year Arabic-literature student living in the city, joined the Farouq as did most of his friends.

The Farouq Brigades emerged from Homs and nearby Rastan just months into the Syrian uprising, now two years old. In the period since, operating under the FSA umbrella, they have formed units across the country, from Daraa in the south near the Jordanian border to the northern region bordering Turkey. The brigades take the name Farouq from Omar bin al-Khatab, a companion of the Prophet Muhammad, political architect of the caliphate and, historically, the second Caliph.

The men recalled their university days with laughter. The mood was light. “I’ve lost so much weight in this revolution,” Bandar said, laughing. “Do you remember how we used to cook in Homs?” Abu Azzam’s specialty was molokhia, green leaves that are carefully picked and turned into a viscous green soup served with chicken and plain rice.

Ramadan recounted an incident that had happened earlier in the day in Raqqa city that TIME also witnessed. He had stopped at a street-side coffee stall in his white pickup truck that has a black flag bearing the Muslim shahada (There is no god but God, and Muhammad is his Prophet) mounted on it. Three teenage girls walked past, two in hijabs, tight jeans and figure-hugging sweaters that extended to their thighs, the third in a black abaya. The third girl looked at the armed men in the truck and brazenly took off her abaya. Under it, she was dressed like her friends. “She must have thought we were Jabhat because of the flag and wanted to make a point!” Ramadan said. “So I turned up the music so she would know that we weren’t.” He continued proudly: “See, this is Raqqa, and the Jabhat thinks it’s going to control it?”

Lunch was cleared and the men said their goodbyes. Abu Mansour, Abu Azzam’s deputy who is also his cousin, walked into the room, bid his cousin farewell and told him he was going to check on his family just across the border in the Turkish town of Akcakale.

Abu Mansour walked the short distance home. His niece had just served steaming-hot Turkish coffee, but before Abu Mansour could take a sip, one of his two cell phones rang. “What! Where are you? I’m coming now!” he said into the phone before jumping up, shoving his local Alhamraa cigarettes and his phones into his leather jacket and rushing out the door. It was a little before 5 p.m. and Abu Azzam had just been shot.

Minutes earlier, on the other side of the border, Abu Azzam had also received a phone call, from one of his men. The Jabhat had set up a random checkpoint at a spot dubbed Liberation Roundabout on the main road in Tal Abyad and were detaining Farouq fighters and trying to disarm them. A few days earlier, 11 Farouq men were picked up by the Jabhat in town.

Abu Azzam grabbed a BKC machine gun and ran out the door to intercede on behalf of his men. According to Em Mohammad, he didn’t ask any of his men to come with him but two followed him anyway. He had just reached the roundabout and stepped out of his car when a member of the Jabhat reportedly tossed a hand grenade in his direction before others opened fire. The melee was over within minutes, and Abu Azzam, as well as several other wounded men, were being ferried by passersby to the border crossing into Turkey, where Abu Mansour was waiting to rush his bloodied commander in a taxi to the local hospital in Akcakale.

The hospital foyer was crowded with unarmed Farouq fighters in plain clothes, as well as others. Em Mohammad paced up and down. She was carrying a blue garbage bag containing her son’s clothes. She held up his indigo jeans. They were bloodied and there was a tear above the right knee.

Abu Azzam was shot in the left side of his abdomen, both his hands were bandaged, and he suffered shrapnel wounds to both legs, as well as above his right eye. One of the Farouq men’s phone rang. “Don’t do anything until we get men and ammunition,” he told the caller. “Calm down! Calm the men down! Here, speak to Em Mohammad and do whatever she says.”

Em Mohammad took the phone. “Please, you are all my sons. This is not the time for rash decisions. We must be smart. Calm down. We are all angry. This has become personal, but we don’t want unnecessary loss of life. Please calm the men down, I’m counting on you.”

Abu Azzam was wheeled into the nearby X-ray room. His mother leaned forward gently through the crowd to cover his naked shoulder with the pale mauve sheet. One of the two Farouq fighters was lying on a gurney in the emergency room. He looked to be about 20 years old and was dressed in military camouflage pants and an aqua T-shirt. He had a shrapnel wound to his left ankle, which was bandaged. Tears welled in his eyes. “They shot Abu Azzam!” he said, before asking one of his colleagues for water, a request denied on doctor’s orders. “Then let me go back out there and fight!” he said, crying. “Let me fight them!”

A gurney with a pale mauve sheet covering a dead man was wheeled out of the emergency room into the foyer, and toward the elevator to be taken to the morgue. The crowd in the foyer gathered around it as the sheet was lifted to reveal the man’s face. He had shoulder-length hair, and also looked to be in his early 20s. Em Mohammad and members of the Farouq didn’t recognize him, but a short man with a closely cropped, graying beard did. The dead man was a member of Jabhat al-Nusra, the short man claimed, before offering the dead man’s name. Em Mohammad started crying. “He’s so young, may God rest his soul,” she said, a generous sentiment given that the man had apparently just tried to kill her son.

Soon after, another dead man was also wheeled out, also identified by the short man as a member of Jabhat al-Nusra. “They have eyes and ears everywhere,” Em Mohammad said, referring to the short man. There were other characters in the foyer, men who were identified to TIME as Turkish intelligence agents. By 6 p.m., four policemen were guarding the entrance of the hospital and using a handheld metal detector to check everyone coming through the doors.

Abu Azzam was to be transferred to a bigger hospital in Sanliurfa some 53 km away. He let out a cry of pain as he was wheeled into a waiting ambulance. A thin stream of fresh blood escaped from under the large bandage over his right eye. (As of Tuesday, the Farouq commander was still in the hospital, under Turkish guard, in stable condition.)

Later on Sunday night, Abu Azzam’s sister and other female relatives crossed into Turkey in the dark, along with their children. They were taken to Abu Mansour’s home. Two Farouq men sat outside the front door, guarding it although they were both unarmed. One, a man in a black-and-gray tracksuit, sat on the stairs. With deep sadness, he said the day’s events had made him want to forget about the revolution. “If this is what it has come to — to us fighting each other — then I want to sit at home and support Bashar,” he said. His view was not shared by most of the Farouq who were itching for a fight.

By Monday, no fewer than five Farouq liwas (or brigades although the term doesn’t strictly correlate to a brigade in the modern military sense) were on their way to Tal Abyad from the provinces of Aleppo and Idlib. There have been clashes in Tal Abyad between the two groups although by Monday afternoon the border crossing was reopened.

Abu Mansour, Abu Azzam’s deputy, said the Jabhat approached him and requested that the matter between the two groups be resolved in a Shari‘a court. As a goodwill gesture, Jabhat released 11 Farouq fighters as well as 22 others they had picked up earlier. They were also forced to retreat out of the various positions they occupied in Tal Abyad to their main base in the town. “The problem is that they have forgotten that we are all fighting Bashar,” Abu Mansour said of the Jabhat. “They want an Islamic emirate. They say that they are Islamists and we are apostates, but we will not accept that they have any sway or authority over us or others. May God heal Abu Azzam, that is the main thing, but in every province now, we will fight them.”